JDSU 21108524 Replacement Battery 7.4V 5200mAh Li-ion

JDSU 21129596 000 / 21100729 000 — 7.4V Li-ion Replacement Battery (21108524)

This is a 7.4V 5200mAh Li-ion replacement battery for JDSU field test instruments, cross-referencing OEM part number 21108524. It fits the 21129596 000, 21100729 000, WiFi Advisor Wireless LAN Analyzer, and Viavi SC-TPS. Voltage and capacity match the original pack exactly.

• Platform fit — 21129596 000, 21100729 000, WiFi Advisor, SC-TPS: These instruments share the same 7.4V battery rail, physical form factor, and BMS handshake protocol. One pack covers the full group without modification.
• Bench tested on actual hardware: We ran this pack through full charge and discharge cycles, monitoring BMS communication, cell balance, and cutoff behaviour under simulated probe initialisation loads. The BMS responded correctly at both ends of the voltage window.
• First-use calibration on JDSU instruments: After installing this pack, run a full calibration cycle through the instrument menu before field deployment. The instrument maps battery state during calibration — skipping this step causes premature low-battery warnings during your first measurement session in the field.

BMS cutoff when the JDSU instrument initialises its probe or wireless module

When the WiFi Advisor or SC-TPS powers up its RF or probe module, it draws a short but sharp current spike — higher than the steady-state load the battery sees during normal logging. An ageing or partially discharged original pack may hit the BMS overcurrent threshold at exactly this moment. The instrument cuts out immediately after the splash screen, which looks like a software fault but is actually a battery protection event. A fresh pack with full cell capacity handles the initialisation spike without tripping the cutoff.

Readings drifting or logging session resetting mid-capture

Sustained sensor load during a long logging session causes a slow voltage sag across the cells. When cell voltage drops below the instrument's internal threshold, the JDSU unit can reset its active session or produce anomalous readings before the low-battery indicator even appears. This happens because the voltage-based fuel gauge lags behind real cell state under load. If sessions are cutting short or data is corrupting, check cell voltage under load — a healthy pack should hold above 7.0V during active measurement. Replace the pack if resting voltage reads above 7.2V but sags below 7.0V the moment the instrument begins a capture.